1. Field of the Invention
The invention relates to a process for producing a twisted elastic thread in which an elastomeric thread of approximately 154 dtex to 310 dtex is adhesively twisted with two yarns. The thickness of which is in each case approximately of 100 to 12,500 dtex. The yarns preferably are OE yarns of polyvinyl chloride, polyvinyl cyanide, polyacrylonitrile and/or wool threads, preferably produced by the rotor process and prior to twisting the yarns are surface-swelled under a vacuum between approximately 0.1 and 0.2 bar in superheated steam at approximately 70.degree. C. for up to ten minutes for loosening purposes, and while twisting is being performed a pre-tension is imparted to the elastomeric thread with respect to the yarns.
2. Description of Relevant Art
Twisted elastic threads generally comprise an elastomeric thread and two yarns of natural or synthetic fibers, which hide this generally undyed elastomeric thread. It was hitherto difficult to produce the elastic twisted threads from inexpensive OE yarns and an elastomeric thread. Thus, OE yarns are produced by the rotor process, are very hard and have an approximately circular cross-section. Such circular yarns do not tend to adhere to the elastomeric thread surface or to remain in the initially occupied position during the stretching apart and drawing together of the elastomeric thread. Instead they slide backwards and forwards on the elastomeric thread, leading after a certain time to the extremely undesired "grinning through" of the not dyed and generally whitish elastomeric thread. Therefore U.S. Pat. No. 2,146,966 proposes adhesion to the elastomeric fiber of yarns which do not automatically adhere thereto with the aid of a suitable, e.g., heat-activatable adhesive. To this end, prior to twisting, the elastomeric thread is provided with a heat-activatable adhesive, is twisted, and after the twisting process is activated by a heat treatment, so that the yarns firmly adhere to the elastomeric thread. Thus, this process always requires adhesive-impregnated yarns which, under certain circumstances, can have unpleasant characteristics, e.g., in the long run the adhesive can change colors, is expensive, in some cases leads to allergies and, particularly at elevated temperatures undesirably reacts with free valencies of man-made fibers.
Thus, DOS 28 11 329 provides an improved process of the present type in which by using yarns roughened and swelled by using steam and which more readily adhere to the elastomeric thread, a good connection with the latter can be ensured without it being necessary to use expensive adhesives, which have a disadvantageous influence on the product quality. The elastomeric thread is preferably twisted under an approximately 3.5 times pre-tension.
It has now been found that in the production of such twisted threads, thread breaks frequently occur when starting and stopping the twister, particularly if a machine must momentarily be switched off while replacing reels or the like.
The problem overcome by the present invention is to prevent such thread breaks during the starting phase of the twister, while retaining the advantages of the process of DOS 28 11 329 and permitting increased productivity with reduced down times.